Molecular Phylogenetics and Evolution

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1 Molecular Phylogenetics and Evolution 55 (2010) Contents lists available at ScienceDirect Molecular Phylogenetics and Evolution journal homepage: Molecular phylogenetic relationships and the evolution of the placenta in Poecilia (Micropoecilia) (Poeciliidae: Cyprinodontiformes) Robert W. Meredith, Marcelo N. Pires, David N. Reznick, Mark S. Springer * Department of Biology, University of California, Riverside, CA 92521, USA article info abstract Article history: Received 12 August 2009 Revised 6 November 2009 Accepted 9 November 2009 Available online 14 November 2009 Keywords: Cyprinodontiformes Poeciliidae Poecilia Micropoecilia Acanthophacelus Placentotrophy Poeciliids are one of the most intensively studied groups within Cyprinodontiformes owing to their use as model organisms for experimental studies on natural and sexual selection, and comparative studies of life-history evolution. Life-history studies have demonstrated multiple origins of placentotrophy and superfetation in poeciliids, including the recent description of placentotrophy in three species of Poecilia (Micropoecilia): P. bifurca, P. branneri, and P. parae. Here, we use a concatenation of seven nuclear gene segments and two mitochondrial segments to examine relationships within Micropoecilia and between this subgenus and other subgenera in Poecilia (Mollienesia, Limia, Pamphorichthys, Acanthophacelus). The combined molecular data set (8668 bp) was analyzed with maximum parsimony, maximum likelihood, and Bayesian methods. We also employed a relaxed molecular clock method to estimate divergence times within Poecilia. All phylogenetic analyses with the combined DNA data set supported the monophyly of Poecilia and recovered a basal split between Poecilia (Acanthophacelus)+ Poecilia (Micropoecilia) and the other three subgenera. Within Micropoecilia, P. bifurca grouped with P. branneri, and these joined P. parae to the exclusion of P. picta. Ancestral reconstructions based on parsimony and Bayesian methods suggest that placentotrophy evolved once in Micropoecilia in the common ancestor of P. bifurca, P. branneri, and P. parae. Divergence time estimates suggest that placentotrophy in Micropoecilia evolved in 64 million years. Ó 2009 Elsevier Inc. All rights reserved. 1. Introduction The family Poeciliidae (Rosen and Bailey, 1963), equivalent to the subfamily Poeciliinae of Parenti (1981), is a diverse group of freshwater fishes in the order Cyprinodontiformes that comprises 220 species in 28 genera (Lucinda, 2003; Lucinda and Reis, 2005). The group includes well-known aquarium fishes such as guppies, mollies, and swordtails (Lucinda and Reis, 2005). Poeciliids are endemic to the New World and are widely distributed throughout the Americas and Caribbean. All poeciliids have internal fertilization and all except Tomeurus are viviparous (Regan, 1913; Rosen and Gordon, 1953; Rosen and Bailey, 1963). Poeciliids are characterized by the presence of a gonopodium that is formed by modified anal-fin rays 3, 4, and 5 (Lucinda and Reis, 2005). Members of the group are frequently used as model organisms for experimental studies on natural and sexual selection (Endler, 1983; Houde, 1997; Schluter et al., 1998; Hamilton, 2001), and comparative studies of life-history evolution that have demonstrated multiple origins of superfetation and placentotrophy (Grove and Wourms, 1991, 1994; Arias and Reznick, 2000; Reznick * Corresponding author. Fax: address: [email protected] (M.S. Springer). et al., 2002, 2007). Most recently, placentotrophy was reported in all populations of P. parae, P. bifurca and P. branneri that were investigated (Pires, 2007; Pires et al., in press). In every case, placentotrophy was documented by a significant increase in embryo dry mass during development, and accompanied by a thickened maternal follicle and enlarged and externalized pericardial membrane in the embryo (Pires et al., in press). Micropoecilia was proposed as a new genus by Hubbs (1926), who included M. bifurca, M. parae, M. picta, M. melanozona, and M. branneri, but also indicated that he was not convinced of the distinctness of any of the species and suggested that all may eventually be united with M. parae. Rosen and Bailey (1963), in their classic monograph on the family Poeciliidae (=Poeciliinae of Parenti, 1981), described the genus Poecilia and its constituent subgenera: Poecilia, Lebistes, Pamphorichthys, and Limia (Table 1). Rosen and Bailey (1963) included Poecilia reticulata (common guppy), the genus Micropoecilia of Hubbs (1926), Poecilia amazonica, and Poecilia scalpridens in the subgenus Lebistes. Micropoecilia parae, M. bifurca, and M. melanzona of Hubbs (1926) were treated as three polymorphs of Poecilia (Lebistes) parae by Rosen and Bailey (1963). Costa (1991) reallocated Poecilia (Lebistes) scalpridens to the subgenus Pamphorichthys. Meyer (1993) reinstated the genus Micropoecilia of Hubbs (1926) for Poecilia parae, P. bifurca, P. picta, /$ - see front matter Ó 2009 Elsevier Inc. All rights reserved. doi: /j.ympev

2 632 R.W. Meredith et al. / Molecular Phylogenetics and Evolution 55 (2010) Table 1 Previous classifications of Poecilia species relevant to this study. Hubbs (1924, 1926) Rosen and Bailey (1963) Meyer, (1993) Poeser et al. (2005) Lucinda and Reis (2005) Family Poeciliidae Family Poeciliidae Family Poeciliidae Family Poeciliidae Family Poeciliidae Subfamily Poeciliinae Subfamily Poeciliinae Subfamily Poeciliinae Subfamily Poeciliinae Subfamily Poeciliinae Tribe Poeciliini Tribe Poeciliini Tribe Poeciliini Tribe Poeciliini Tribe Poeciliini Genus Limia Genus Poecilia Genus Poecilia Genus Poecilia Genus Poecilia Genus Micropoecilia P. (Poecilia) caucana P. (Lebistes) reticulata P. (Acanthophacelus) Genus Limia reticulata M. bifurca P. (Poecilia) latipunctata P. (Pamphorichthys) P. (Acanthophacelus) wingei Genus Micropoecilia M. picta P. (Lebistes) reticulata Genus Micropoecilia P. (Micropoecilia) parae Genus Pamphorichthys M. branneri P. (Lebistes) parae [included M. bifurca P. (Micropoecilia) branneri Micropoecilia bifurca] M. parae P. (Lebistes) picta M. picta P. (Micropoecilia) bifurca M. melanzona P. (Lebistes) branneri M. branneri P. (Micropoecilia) picta Genus Lebistes P. (Pamphorichthys) minor M. parae P. (Micropoecilia) minima L. reticulatus P. (Limia) dominicensis Genus Mollienisia a P. (Limia) melanogaster Genus Allopoecilia A. caucana Tribe Pamphoriini Genus Pamphorichthys a Hubbs (1924, 1926) used Mollienisia rather than Mollienesia. Bailey and Miller (1950) subsequently provided justification for using Mollienesia instead of Mollienisia. P. amazonica and P. branneri based on three derived morphological characters: (1) variegated males and females; most specimens with a relatively well-developed dark humeral spot on the side of the body; (2) males with anal-fin rays 6 and 7 and ventral fins extending to the base of the gonopodium palp; and (3) ray 3 of the gonopodium with rose thorn-like spines. Within Micropoecilia, Meyer (1993) also proposed synapomorphic characters for M. bifurca and M. picta, these two plus M. parae, and these three plus M. amazonica. Meyer (1993) also defined Poecilia (Lebistes) as a monotypic subgenus that included only P. reticulata. Meyer s (1993) M. amazonica is of questionable taxonomic value because its type series is composed of a combination of M. branneri and M. parae individuals (C.A. Figueiredo, pers. comm. to M. Pires). Subsequent to Meyer (1993), Costa and Sarraf (1997) described Poecilia (Lebistes) minima and hypothesized a close relationship of this taxon to P. branneri based on five morphological synapomorphies. Costa and Sarraf (1997) also challenged Meyer s (1993) putative synapomorphies for Micropoecilia and argued that (1) the variegated pattern does not occur in both sexes, (2) the humeral spot is not present in all species, and (3) the morphological features of the anal-fin rays and third gonopodial ray are also present in other groups. Given these differences with Meyer (1993), Costa and Sarraf (1997) did not concur with Meyer s (1993) reinstatement of Micropoecilia and questioned the monophyly of this genus. Breden et al. (1999) examined relationships among representatives of the major divisions of the genus Poecilia using mitochondrial ND2 sequences. Breden et al. (1999) included two species of Micropoecilia (sensu Meyer, 1993), M. picta and M. parae, which grouped together and were the sister taxon to Poecilia reticulata. Similarly, Hrbek et al. (2007) and Lucinda and Reis (2005) found support for an association of P. reticulata with representative species of Micropoecilia based on a multigene concatenation and a matrix of osteological and soft anatomical characters, respectively. Poeser et al. (2005) described Poecilia wingei (the Endler s livebearer, Campoma guppy, or Cumaná guppy), a close relative of Poecilia (Lebistes) reticulata, and placed both species in the subgenus Acanthophacelus rather than Lebistes. Poeser et al. (2005) argued that apparent autapomorphies of P. reticulata were instead synapomorphies of P. reticulata and P. wingei, and grouped these species in the subgenus Acanthophacelus. Poeser et al. (2005) chose Acanthophacelus rather than Lebistes because the latter name is tied to a molly, not the guppy, and is not available as a subgenus name for P. reticulata (Poeser and Isbrücker, 2002). Acanthophacelus Eigenmann, 1907 then becomes the first available subgenus name for P. reticulata (Poeser and Isbrücker, 2002). Shories et al. (2009) described Poecilia (Acanthophacelus) obscura, which represents a third species in the subgenus Acanthophacelus. Poeser et al. (2005) also placed all of Meyer s (1993) Micropoecilia species and the newly described Poecilia (Lebistes) minima of Costa and Sarraf (1997) into Poecilia (Micropoecilia) (see Table 1). In the present study we use a combined mitochondrial and nuclear DNA data set to examine relationships among species in Poeser et al. s (2005) subgenus Micropoecilia (bifurca, branneri, parae, picta). Our study includes all of the placentotrophic Micropoecilia species reported by Pires et al. (in press), as well as representatives of most of the other major subdivisions of Poecilia. This taxon sampling provides a basis for (1) evaluating the monophyly of Poecilia (Micropoecilia), (2) determining the number of origins of placentotrophy in Poecilia (Micropoecilia), and (3) examining relationships among the major lineages within the genus Poecilia. 2. Methods and materials 2.1. Taxon sampling We included all recognized species of Poecilia (Micropoecilia) except for P. minima. We also included two representatives each from the Poecilia subgenera Acanthophacelus, Limia, Mollienesia, and Pamphorichthys. Two species of Cnesterodon were included as outgroups. A previous molecular study that included both mitochondrial and nuclear loci demonstrated that Cnesterodon is the closest outgroup to Poecilia (Hrbek et al., 2007). All ingroup and outgroup taxa are listed in Supplementary Information Table Gene sequences QUIAGEN DNeasy Tissue extraction kits were used to extract genomic DNA from the skeletal muscle of 95% ethanol-preserved specimens. Two mitochondrial and seven nuclear gene regions were amplified. The first mitochondrial segment included the 3 0

3 R.W. Meredith et al. / Molecular Phylogenetics and Evolution 55 (2010) end of trna Glu, the complete cytochrome b (cytb) gene, and the 5 0 end of trna Thr. The second segment consisted of the 3 0 end of trna Gln, all of trna Met, the complete NADH dehydrogenase subunit 2 gene (NADH2), all of trna Trp, all of trna Ala, and the 5 0 end of trna Asn. The nuclear regions included two partial exons (8 and 10), all of exon 9, and two introns (8 and 9) of the tyrosine kinase gene (X-src); exon 1 of myosin, heavy polypeptide 6 (myh6); exon 2 of ectodermal-neural cortex 1 like protein (ENC1); exon 2 of glycosyltransferase (Glyt); exon 1 of SH3 and PX domain containing 3 (SH3PX3); a portion of the 7 transmembrane receptor region of rhodopsin (Rh); and exon 3 of recombination activating gene-1 (Rag1). The nuclear markers Rh, X-src, myh6, ENC1, Glyt, SH3PX3, and Rag1 are located on chromosomes 8, 17(?), 20, 5, 16, 25, and 25, respectively, of the zebrafish Danio rerio. Sequences for most PCR primers used in this study have previously been published. New internal and external primers were designed as necessary to amplify problematic taxa. Sequences for new primers, previously used primers, and primer combinations used in amplifications are provided in Supplementary Information Table 2. Previously described primers used in this study include those for X-src (Meyer and Lydeard, 1993); MYH6, ENC1, Glyt, and SH3PX3 (Li et al., 2007); Rh (Chen et al., 2003); Rag1 and NADH2 (Hrbek et al., 2007; Kocher et al., 1995; Ptacek and Breden, 1998; Breden et al., 1999); and cytb (Schmidt et al., 1998). Nested PCRs were carried out following the protocols outlined in Li et al. (2007) for myh6, ENC1, Glyt, and SH3PX3. All other genes were amplified using the following protocol: initial denaturation at 94 C for 2 min; 35 cycles of 1 min at 94 C (denaturation), 1 min at 50 C (annealing), and 1 min at 72 C (extension); and a final extension of 10 min at 72 C. In all cases PCR products were run out on a 1% agarose gel and the product of interest was then excised and cleaned using QIAGEN QIAquick PCR purification kits. Products were then sequenced in both directions at the University of California Riverside s Core Genetics Institute, which uses an automated DNA sequencer (ABI 3730xl). Sequencing primers were designed as necessary. All accession numbers for both the 136 new and 17 previously published sequences are given in Supplementary Information Table DNA alignments and data compatibility We used the program SOAP v1.2a4 (Löytynoja and Milinkovitch, 2001), with gap opening (11 19) and gap extension (3 11) penalties in steps of two, to identify alignment-ambiguous regions. These settings correspond to those that were used by Gatesy et al. (1993). Alignment-ambiguous regions were excluded from phylogenetic analyses. The appropriateness of combining the individual gene segments into a combined data set was tested using (1) the partition homogeneity test (Farris et al., 1994; Swofford, 2002) with each combination of partitions outlined below, 0 replications, and taxon input orders per replicates, and (2) the bootstrap compatibility method (de Queiroz, 1993; Teeling et al., 2000) with 500 bootstrap replicates and a 90% bootstrap support criterion. ML bootstrap compatibility tests allowed each segment to have its own model of sequence evolution as suggested by the Akaike Information Criterion of Modeltest 3.06 (Posada and Crandall, 1998). We used three different schemes to partition the data as follows: (1) two nuclear partitions (exons and introns) and two mitochondrial partitions (protein-coding and trna); (2) four nuclear partitions (1st codon positions, 2nd codon positions, 3rd codon positions, introns) and four mitochondrial partitions (1st codon positions, 2nd codon positions, 3rd codon positions, trna); and (3) eight nuclear partitions (one for coding sequences from each of seven different genes and one for X-src introns) and three mitochondrial partitions (NADH2, cytb, trna genes). Models for individuals partitions were as follows: K80+I (ENC1); HKY+C (Glyt); TrN+I (SH3PX3, myh6, Rh, 2nd mitochondrial codon positions); GTR+I+C (Rag1, NADH2, 3rd mitochondrial codon positions); K80+I+C (X-src exons); TVM+I (X-src introns, 1st and 2nd nuclear codon positions); TVM+I+C (cytb); TrN+I+C (exons); TVM+I+C (mitochondrial protein-coding); K81uf+I+C (trnas); TVM+C (3rd nuclear codon positions); GTR+C (1st mitochondrial codon positions). Both the bootstrap compatibility method and the partition homogeneity test (four partitions, p = 0.673; eight partitions, p = 0.500; 11 partitions, p = 0.820) suggested that it was appropriate to combine the individual segments into one multigene data set Phylogenetic analyses PAUP 4.0b10 (Swofford, 2002), RAxML (Stamatakis, 2006), and MrBayes V3.1.1 (Huelsenbeck and Ronquist, 2001; Ronquist and Huelsenbeck, 2003) were used to perform maximum parsimony (MP), maximum likelihood (ML), and Bayesian analyses, respectively, on three data sets: (1) the combined data set that included seven nuclear segments and two mitochondrial segments (length = 8668 bp); (2) the combined nuclear data set (length = 6159 bp); and (3) the combined mitochondrial data set (length = 2509 bp). Gaps were treated as missing data in all analyses. Branch and bound analyses were employed to find the shortest tree(s) in MP analyses. MP bootstrap analyses (0 replications) employed heuristic searches with 0 randomized taxon addition sequences and tree-bisection and reconnection branch swapping. ML and Bayesian analyses were performed with the three partitioning schemes outlined above with models suggested by Modeltest 3.06 (Posada and Crandall, 1998). ML analyses with RAxML employed 500 replicates, randomized MP starting trees, and the fast hill-climbing algorithm; all other free parameters were estimated. MrBayes v3.1.1 (Huelsenbeck and Ronquist, 2001; Ronquist and Huelsenbeck, 2003) was used to calculate Bayesian posterior probabilities. MrBayes carries out Metropolis-coupled Markov chain Monte Carlo sampling. Bayesian analyses employed eight Markov chains (seven hot, one cold), with random starting trees, default priors, and chain sampling every 0 generations. Analyses were terminated once the average standard deviation of split frequencies for the simultaneous analyses fell below If the model suggested by Modeltest 3.06 was not available in MrBayes, the next most complex model was used Molecular dating analyses The likelihood ratio statistic rejected the molecular clock (p < 0.05) for 11 of the 19 possible partitions (cytb, NADH2, mitochondrial protein-coding genes, ENC1, Rag1, X-src exons, nuclear exons, nuclear 2nd codon positions, nuclear 3rd codon positions, mitochondrial 1st codon positions, mitochondrial 3rd codon positions). Therefore, we employed the relaxed molecular clock method implemented in BEAST ver (Drummond et al., 2006; Drummond and Rambaut, 2007), which allows for complex models of evolution and soft node constraints (Hedges and Kumar, 2004; Yang and Rannala, 2006). We used the uncorrelated lognormal distribution (UCLN) model, which draws the rate of each lineage independently from a lognormal distribution. Models of molecular evolution were from Modeltest 3.06 (Posada and Crandall, 1998). In cases where the model selected by Modeltest was not available in BEAST (i.e., models with three to five categories for substitution rates), we used the next most general model (i.e., GTR). For each partition scheme, three independent analyses were run for ten million generations. The three runs were combined using Log-Combiner; Tracer 1.4 (Rambaut and Drummond, 2003) was used to inspect for stationarity/mixing and to confirm that the estimated sample size for each parameter was greater than 200. Given the

4 634 R.W. Meredith et al. / Molecular Phylogenetics and Evolution 55 (2010) lack of a fossil record for taxa included in our analyses, we used a secondary constraint taken from Hrbek et al. (2007), who reported a minimum of mya and a maximum of mya for most recent common ancestor of Pamphorichthys, Limia, and Mollienesia. We employed a soft constraint, which followed a normal distribution, with 95% of the normal distribution between the specified minimum and maximum given in Hrbek et al. (2007) Ancestral state reconstructions Parsimony and SIMMAP Version 1.0 B2.3.2 (Bollback, 2006) were used to estimate ancestral states for lecithotrophy versus placentotrophy. Terminal taxa included all species of Acanthophacelus and Micropoecilia that were included in our phylogenetic analyses. The relative amounts of pre- and post-fertilization maternal provisioning to embryos have been quantified for all of these taxa (Pires et al., in press) and indicate that P. reticulata, P. wingei and P. picta embryos lost weight during development and that all or most of the resources necessary for embryonic growth were provided by females in the form of yolk (lecithotrophy); in contrast, P. parae, P. bifurca, and P. branneri females exhibited extensive post-fertilization resource allocation to embryos via a follicular placenta (placentotrophy). SIMMAP implements the procedures of Nielsen (2002) and Huelsenbeck et al. (2003) for stochastically mapping mutations on phylogenies. SIMMAP uses a fully Bayesian approach with Markov chain Monte Carlo sampling to calculate a posterior probability distribution that accommodates uncertainty in ancestral states, evolutionary rates, and the phylogeny. We used all post burnin Bayesian trees (5957 trees) from the combined MrBayes analysis (11 partitions). SIMMAP employs a C distribution prior on the overall substitution rate of the morphological character. The parameters of the C distribution are a and b, and these parameters describe the mean (a/b) and variance (a/b 2 ) of the distribution. We used 60 discrete categories to describe the C distribution of the rate prior. For two-state morphological characters SIMMAP uses an additional prior the bias parameter. The bias parameter is a symmetrical beta distribution that is described by a single parameter, a, and was approximated with 19 categories. Branch length proportionality was maintained by rescaling branch lengths before the priors were applied. Ancestral state reconstructions were performed with three different combinations of parameters for the C distribution prior: a =1,b =1;a =3,b = 2; and a =5,b = 5. The bias parameter prior was specified with a = 1, which specifies an uninformative prior with equal prior probabilities. The number of draws from each prior distribution was set at ten. 3. Results 3.1. Sequence alignments and sequence variability The combined alignment included 8668 bp after excluding alignment-ambiguous regions of trna (6 bp) and X-src (15 bp). The nuclear and mitochondrial components of the combined data set were 6159 and 2509 bp in length, respectively. The nuclear data included 371 (=6.0%) parsimony-informative sites [52 (=2.6%) at 1st codon positions; 24 (1.2%) at 2nd codon positions; 266 (=13.4%) at 3rd codon positions; and 29 (=12.8%) at intronic positions]. The mitochondrial data included 774 (=30.8%) parsimony-informative sites [164 (=22.5%) at 1st codon positions; 41 (=5.6%) at second codon positions; 538 (=73.8%) at 3rd codon positions; and 32 (=9.8%) at trna positions]. Among coding sequences for individual nuclear genes, parsimony-informative sites ranged from 4.7% (Glyt and SH3PX3) to 7% (Rag1). Rescaled consistency (RC) and retention index (RI) values were both higher for the nuclear data (0.65, 0.81) than the mitochondrial data (0.30, 0.58). Table 2 summarizes information on partition length, the number of constant and variable (parsimony-uninformative and parsimonyinformative) characters in each partition, the contribution to the length of the most-parsimonious tree for the combined data set (see below) that derives from each partition, RC, and RI. The number of changes per site was also calculated for different genes/partitions and ranged from 0.02 (2nd codon positions of nuclear genes) to 2.60 (3rd codon positions of mitochondrial genes) (Table 2) Phylogenetic analyses Fig. 1 shows the single most-parsimonious tree (3325 steps) that was recovered with the combined data set. RAxML analyses with four, eight, or 11 partitions resulted in ML trees that were topologically identical to each other (Fig. 2). The ML trees differed from the MP tree in grouping Poecilia (Limia) and Poecilia (Pamphorichthys) to the exclusion of Poecilia (Mollienesia). Fig. 2 also shows mean Bayesian posterior probabilities (BPP) based on two independent runs above the branches, and ML Bootstrap Support Percent- Table 2 Parsimony statistics for different partitions. Partition Partition length Number of constant characters Number of variable, uninformative characters Number of informative characters Rescaled consistency index Retention index Number ofsteps on globally mostparsimonious tree Nuclear Nuclear 1st codon Nuclear 2nd codon Nuclear 3rd codon Introns ENC Glyt SH3PX MYH Rag Rh X-src X-src exon Mitochondrial Mitochondrial 1st codon Mitochondrial 2nd codon Mitochondrial 3rd codon Mitochondrial trnas Cytb NADH Number of changes per site on globally most-parsimonious tree

5 R.W. Meredith et al. / Molecular Phylogenetics and Evolution 55 (2010) Cnesterodon decemmaculatus Cnesterodon hypselurus Poecilia (Limia) dominicensis Poecilia (Limia) melanogaster Poecilia (Mollienesia) caucana Poecilia (Mollienesia) latipunctata Poecilia (Pamphorichthys) araguaiensis Poecilia (Pamphorichthys) minor Poecilia (Micropoecilia) bifurca Poecilia (Micropoecilia) branneri Poecilia (Micropoecilia) parae French Guyana Poecilia (Micropoecilia) parae Suriname Poecilia (Micropoecilia) picta Venezuela Poecilia (Micropoecilia) picta Trinidad Poecilia (Acanthophacelus) reticulata Poecilia (Acanthophacelus) wingei changes Poecilia (Acanthophacelus) wingei Venezuela Fig. 1. The shortest tree (3326 steps) for the combined data set based on analyses with PAUP 4.0b10 (Swofford, 2002). ages (BSPs) below the branches for analyses with 11 partitions. All of the topological relationships shown in Fig. 2 were also recovered in Bayesian analyses of the combined data set with four or eight partitions. Table 3 summarizes bootstrap support percentages based on MP and ML analyses, and BPP values based on Bayesian analyses with four, eight, and 11 partitions. All species, subgenera, and genera were recovered as monophyletic (% BSP and 1.00 BPP). Within the genus Poecilia, there was a basal split between Limia + Mollienesia + Pamphorichthys and Micropoecilia + Acanthophacelus. Within Micropoecilia, all clades were strongly supported (% BSP and 1.00 BPP). Poecilia (Micropoecilia) bifurca grouped with P. (M.) branneri, these two were sister to P. (M.) parae, and this clade was the sister-group to P. (M.) picta. Bayesian trees supported an association of Limia and Pamphorichthys to the exclusion of Mollienesia, whereas MP and ML bootstrap analyses favored an association of Limia and Mollienesia to the exclusion of Pamphorichthys. Analyses based on the nuclear and mitochondrial data sets are generally concordant with the combined data set, but support values for some nodes are less robust (Supplementary Information Figs. 1 and 2; Supplementary Information Tables 3 and 4). In contrast to analyses with the combined and nuclear data sets, analyses with the mitochondrial data set (MPP tree shown in Fig. 4) excluded Poecilia (Micropoecilia) picta from a clade containing all other Poecilia (Micropoecilia) species plus Poecilia (Acanthophacelus). The mitochondrial MP tree differed from the ML and MPP mitochondrial trees in recovering Pamphorichthys as the sister taxon to all other ingroup taxa. Two synapomorphic indels were discovered. First, a six bp deletion in Glyt ( in concatenation) is shared by all species belonging to Micropoecilia and Acanthophacelus. Second, a seven bp deletion ( in concatenation) in intron 9 of X-src is shared by both Poecilia (Micropoecilia) picta individuals Molecular dating analyses A chronogram based on molecular dating analyses with BEAST v1.4.8 is shown in Fig. 3. Point estimates of divergence times, along with 95% highest posterior densities, are given in Supplementary Information Table 5. The base of Poecilia was dated at 26 mya. Within Poecilia, the split between Acanthophacelus and Micropoecilia was dated at mya. The most recent common ancestor of Poecilia (Micropoecilia) was dated at 18 mya. Within this subgenus, P. parae diverged from P. bifurca + P. branneri at mya, and the latter two species split at 8 9 mya.

6 636 R.W. Meredith et al. / Molecular Phylogenetics and Evolution 55 (2010) Cnesterodon decemmaculatus Cnesterodon hypselurus Poecilia (Limia) dominicensis 54 Poecilia (Limia) melanogaster 17 Poecilia (Pamphorichthys) araguaiensis Poecilia (Pamphorichthys) minor Poecilia (Mollienesia) caucana Poecilia (Mollienesia) latipunctata Poecilia (Micropoecilia) bifurca Poecilia (Micropoecilia) branneri Poecilia (Micropoecilia) parae French Guyana Poecilia (Micropoecilia) parae Suriname Poecilia (Micropoecilia) picta Venezuela Poecilia (Micropoecilia) picta Trinidad Poecilia (Acanthophacelus) reticulata 0.05 changes Poecilia (Acanthophacelus) wingei Poecilia (Acanthophacelus) wingei Venezuela Fig. 2. ML phylogram (ln likelihood = ) obtained with RAxML for the combined data set with 11 partitions. Mean Bayesian posterior probabilities (BPPs) based on two independent runs and ML bootstrap support percentages (BSPs) are shown above and below branches, respectively Ancestral state reconstructions Fig. 4 shows the posterior probabilities of the reconstructed ancestral states for lecithotrophy and placentotrophy using rate parameter priors of a = 3 and b = 2 for the C distribution, and an uninformative prior on the bias parameter (a = 1). Parsimony ancestral state reconstructions are also shown in Fig. 4. Supplementary Information Table 6 gives the posterior probabilities of the reconstructed ancestral states (lecithotrophy, placentotrophy) for analyses with each combination of priors that were employed. The three different combinations of priors gave posterior probabilities that differed by no more than at a given node. The ancestral state reconstruction based on parsimony indicates that placentotrophy evolved once in Poecilia (Micropoecilia) in the common ancestor of P. parae, P. bifurca, and P. branneri. SIM- MAP reconstructions also support a single origin of placentotrophy in the common ancestor of these species, but with less certainty. Table 3 Bootstrap support percentages (ML and MP) and Bayesian posterior probabilities for analyses with the combined data set. Nodes in Fig. 1 that were supported by % bootstrap percentages in MP and ML analyses, and 1.00 posterior probabilities in Bayesian analyses, are not reported. Node MP ML Bayesian Four Partitions Eight Partitions 11 partitions Four Partitions Eight Partitions P. (Pamphorichthys)+P. (Limia)+P. (Mollienesia) P. (Limia)+P. (Mollienesia) P. (Pamphorichthys)+P. (Limia) P. (Limia)+P. (Mollienesia)+P. (Micropoecilia)+P. (Acanthophacelus) partitions

7 R.W. Meredith et al. / Molecular Phylogenetics and Evolution 55 (2010) Poecilia (Acanthophacelus) wingei Poecilia (Acanthophacelus) wingei Venezuela Poecilia (Acanthophacelus) reticulata Poecilia (Micropoecilia) picta Venezuela Poecilia (Micropoecilia) picta Trinidad Poecilia (Micropoecilia) bifurca Poecilia (Micropoecilia) branneri Poecilia (Micropoecilia) parae French Guyana Poecilia (Micropoecilia) parae Suriname Poecilia (Limia) dominicensis Poecilia (Limia) melanogaster Poecilia (Pamphorichthys) araguaiensis Poecilia (Pamphorichthys) minor Poecilia (Mollienesia) caucana Poecilia (Mollienesia) latipunctata Cnesterodon decemmaculatus Oligocene Miocene Plio. Pl. Paleogene Neogene CENOZOIC Million Years Ago 10 0 Cnesterodon hypselurus Fig. 3. A timeline in millions of years before present for Poecilia evolution based on analyses with BEAST and the combined data set (11 partitions). Grey bars indicate 95% highest posterior densities (HPDs). The open circle denotes the node that was used to calibrate divergence times (see text). Plio. = Pliocene; Pl. = Pleistocene. SIMMAP Parsimony Lecithotrophic Placentotrophic Poecilia (Micropoecilia) bifurca Poecilia (Micropoecilia) branneri Poecilia (Micropoecilia) parae French Guyana Poecilia (Micropoecilia) parae Suriname Poecilia (Micropoecilia) picta Venezuela Poecilia (Micropoecilia) picta Trinidad Poecilia (Acanthophacelus) reticulata Poecilia (Acanthophacelus) wingei Poecilia (Acanthophacelus) wingei Venezuela Fig. 4. SIMMAP (circles) and parsimony (squares) reconstructions for placentotrophy and lecithotrophy in Poecilia (Acanthophacelus) and Poecilia (Micropoecilia).

8 638 R.W. Meredith et al. / Molecular Phylogenetics and Evolution 55 (2010) Discussion 4.1. Mitochondrial versus nuclear data The mitochondrial data set exhibits much more variation than the nuclear data set. The average number of substitutions per site for the mitochondrial data set is 7.8-fold higher than for the nuclear data set (Table 2). The fastest-evolving partition of the mitochondrial data set (3rd codon positions) is 130-fold faster than the slowest-evolving partition of the nuclear data set (2nd codon positions) (Table 2). Whereas the mitochondrial sequences are evolving faster and contain a larger percentage of parsimony-informative sites than nuclear sequences, the nuclear data exhibit less homoplasy based on RC and RI values. Even with these differences, trees based on the mitochondrial and nuclear data sets provide robust support for many of the same clades (e.g., Limia, Mollienesia, Pamphorichthys, Acanthophacelus). There are also instances of congruence, but with one of the two data sets providing much stronger support than the other data set. Mitochondrial data provide robust support for the monophyly of Micropoecilia + Acanthophacelus, but only moderate support for Mollienesia + Pamphorichthys + Limia. In contrast, nuclear data provide stronger support for Mollienesia + Pamphorichthys + Limia, but weaker support for Acanthophacelus + Micropoecilia. Within Micropoecilia + Acanthophacelus, nuclear data provide stronger support for Micropoecilia monophyly than mitochondrial data. Together, the mitochondrial and nuclear data sets complement each other and yield a robust phylogeny for almost all nodes. The inclusion of gene regions that evolve at different evolutionary rates maximizes the likelihood of obtaining phylogenetic resolution at both shallow and deep levels in a phylogenetic tree (Hrbek et al., 2007) Phylogenetic relationships Hubbs (1926) erected the genus Micropoecilia and included five species (M. bifurca, M. parae, M. picta, M. melanzona, M. branneri) inthis genus. Rosen and Bailey (1963) folded Micropoecilia Hubbs, 1926 into the subgenus Poecilia (Lebistes) along with P. reticulata, P. amazonica, and P. scalpridens. Micropoecilia was reinstated by Meyer (1993). Subsequently, the monophyly of this group has been challenged (Costa and Sarraf, 1997) and also supported (Figueiredo, 2003; pers. comm.) based on analyses of morphological characters. Most recently, Poeser et al. (2005) recognized five species (P. parae, P. branneri, P. bifurca, P. picta, P. minima) in the subgenus Poecilia (Micropoecilia). The present study is the most comprehensive molecular phylogenetic study to date on Micropoecilia, both in terms of taxonomic representation and gene sampling. We included four of five Micropoecilia species recognized by Poeser et al. (2005), all of which were originally included in Micropoecilia when it was proposed as a new genus by Hubbs (1926). Our results corroborate Meyer s (1993) hypothesis that Micropoecilia is monophyletic. Within Micropoecilia, our molecular phylogeny is discordant with Meyer s (1993) morphological phylogeny. Meyer (1993) proposed a sister-group relationship between M. bifurca and M. picta, a sistergroup relationship between these two and M. parae, and a basal split between M. branneri and all other species of Micropoecilia. Each of these hypotheses is supported by one or more putative gonopodial synapomorphies (Meyer, 1993). In contrast, our results support a sister-group relationship between M. bifurca and M. branneri, a sistergroup relationship between these two and M. parae, and a basal split between M. picta and all other species of Micropoecilia (Figs. 1 and 2). Our results also provide support for a sister-group relationship between Micropoecilia and Acanthophacelus and corroborate previous morphological (Lucinda and Reis, 2005) and molecular (Breden et al., 1999; Hamilton, 2001; Hrbek et al., 2007) studies that have supported this hypothesis. In addition, our results confirm Poeser et al. s (2005) hypothesis that Poecilia wingei, which was described after Rosen and Bailey s (1963) publication, is the sister taxon to Poecilia reticulata. Finally, our results are consistent with a clade comprising Limia, Mollienesia, and Pamphorichthys as in Hamilton (2001) and Hrbek et al. (2007). However, we interpret this result with caution given our incomplete taxonomic sampling for these lineages. Our analyses failed to resolve relationships among Pamphorichthys, Limia, and Mollienesia, whereas Hrbek et al. (2007) reported a high posterior probability (0.97) for a sister-group relationship between Limia and Pamphorichthys. In contrast to Hamilton (2001), Hrbek et al. (2007), and our own molecular results, Lucinda and Reis (2005) found that Pamphorichthys was more closely related to Micropoecilia and Acanthophacelus than to Limia based on morphological data. Lucinda and Reis (2005) listed seven characters that diagnose this clade, but also noted that all of these characters were not uniquely derived and/or reversed features (p. 46) The evolution of placentotrophy in Micropoecilia Within Poeciliidae, placentotrophy has evolved in Heterandria formosa (Grove and Wourms, 1991, 1994), Phalloceros caudimaculatus (Arias and Reznick, 2000), Xenodexia ctenolepis (Reznick et al., 2007), and three times within the genus Poeciliopsis (Reznick et al., 2002). Pires et al. (in press) documented yet another independent origin of placentotrophy in Poecilia (Micropoecilia). Specifically, placentotrophy occurs in P. branneri, P. bifurca, and P. parae, but not in P. picta. Our results provide robust support for the monophyly of P. branneri, P. bifurca, and P. parae within Micropoecilia. Ancestral state reconstructions support the hypothesis that placentotrophy evolved in the common ancestor of these taxa. The branch on which placentotrophy evolved extends from 18 to mya, and establishes a maximum time interval of 3 4 myr for the evolution of placentotrophy. Reznick et al. (2002) reported maximum time intervals of 2.36 and 0.75 million years for the evolution of placentotrophy in two different clades of Poeciliopsis Taxonomic recommendations An important debate in poeciliid systematics is whether to treat Poecilia as a genus with multiple subgenera (e.g., Rosen and Bailey, 1963) or to elevate each subgenus to the level of genus. In our view, resolution of this debate hinges on maintaining the scientific name Poecilia reticulata for the common guppy, which has been and remains a model organism for scientific studies. This stability is maintained if we follow a modified version of Rosen and Bailey s (1963) taxonomic scheme that recognizes multiple subgenera in the genus Poecilia. Accordingly, we support a taxonomy that recognizes Acanthophacelus, Micropoecilia, Limia, Pamphorichthys, and Mollienesia as subgenera in the genus Poecilia for taxa that were included in our study. Whereas each of these subgenera has been recognized in one or more modern classifications [e.g., Rosen and Bailey (1963) recognized Limia, and Pamphorichthys; Meyer and Radda (2000) recognized Mollienesia; Poeser et al. (2005) recognized Acanthophacelus and Micropoecilia], they have never been recognized as monophyletic subgenera in the same classification. Our recognition of these subgenera is based on phylogenetic analyses of the most comprehensive molecular data set yet published for representative taxa in the genus Poecilia. Rosen and Bailey (1963) included mollies and P. vivipara in the subgenus Poecilia rather than Mollienesia, but molecular studies (Breden et al., 1999; Hamilton, 2001) suggest that Rosen and Bailey s (1963) subgenus Poecilia is polyphyletic, and that P. vivipara represents a distinct lineage within the genus Poecilia that is separate from mollies. We therefore recommend placing mollies in the subgenus Mollienesia, and retaining the subgenus

9 R.W. Meredith et al. / Molecular Phylogenetics and Evolution 55 (2010) Poecilia for Poecilia vivipara. Breden et al. (1999) and Hamilton (2001) also found that P. vivipara is separate from P. reticulata. In contrast to the taxonomic approach that we recommend, which will maintain taxonomic stability for P. reticulata, elevation of subgenera to the generic level will necessitate moving Poecilia reticulata to a different genus (i.e., Acanthophacelus) because P. vivipara represents a distinct lineage based on other molecular studies (Breden et al., 1999; Hamilton, 2001) and is the type species for the genus Poecilia. If subgenera are elevated to genera, P. vivipara has priority and will retain the genus name Poecilia. Acknowledgments We thank F. Breden, Heather Alexander, J. de Greef, M. Schartl, and the São Paulo University Museum of Zoology, Brazil (MZUSP), in particular M. de Pinna, C.R. Moreira, and C.A. Figueiredo for providing some of the specimens used in this work. 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